You are correct, anyone 23 and over in the minors is rule 5 eligible, but I doubt anyone will swipe him in the rule 5 draft, since he really isn't anywhere near Major League ready.
Considering that this is what our 40 man roster looks like (have a puke bag ready), I don't think keeping him there will be a problem, if he makes progress this year.

Yes, but 3-4 years? At some point, you'd hope we'd have legitimate prospects taking up the extra 15 slots. Not guys that spent five years hitting .250 in low minor league ball with little speed or defensive capability. Yeah, this guy had promise. Five years ago. His injury didn't set him back, he's been pretty awful overall.